The invention relates to a hydraulic device for producing a force to be applied to a component, either below or beyond the elastic limit of the material forming the component. A device of this kind can be used e.g. for tightening bolts and nuts at high torques.
In the manufacture of boiler components and mechanical appliances, it is conventional to tighten nuts and bolts mechanically at torques which may be in excess of 250 kg/meters. In order to reduce the labor of manual tightening, which requires considerable muscular effort, it has been proposed to provide a hydraulic tightening device which utilizes hydraulic energy to provide a tightening torque. This prior proposed device has a ratchet wheel driven by a pawl actuated by the piston of a hydraulic jack. A square peg secured to the ratchet wheel is connected to the bolt (or nut) to be tightened by means of a clamp or the like and the bolt is driven and thus tightened by a series of extension and retraction cycles of the jack piston. This prior proposed device has two main disadvantages. The first is that it takes a relatively long time for the initial tightening of the bolt since a number of extension and retraction cycles of the piston (normally a dozen) are required for each complete revolution of the nut or bolt. Consequently, a very large number of outward and return cycles of the jack piston are required before the device is retained in position by itself on the bolt (or nut) being tightened, by virtue of the torque applied to the bolt, and the resultant reaction force. During this initial phase, the workman has to hold the device in his hand until a reaction force is produced which holds the tool in position before final tightening. During each retraction stroke of the piston the reaction force falls to zero and the workman has to hold the device unless it stays in position through its own weight. A second disadvantage of the known device is that the ratchet wheel may not catch easily or operate reliably at the end of the stroke of the jack piston, when tightening is relatively complete. This is because the remaining piston stroke may then be insufficient for the pawl to move from one tooth to the next on the ratchet wheel and catch so that tightening can be completed. Experience has shown that, at this stage, the device often jams and cannot be released from the bolt. In addition, the prior device is inefficient during the initial tightening since it is adapted to withstand high pressures whereas, during the initial phase, it operates at low pressure and is therefore considerably over dimensioned.